There are no additives that can be used on flat serpentine belts. They will make dirt stick to the belt and cause even more squealing. The belt needs to be replaced now and the pulleys must be scrubbed to remove any soap residue.
There are two potential causes of squealing. A pulley is tipped or turned causing the belt to walk across it as it goes around it. That is most commonly caused by an idler pulley with bad bearings. The belt could also be loose. Most commonly that is caused by a spring-loaded tensioner pulley that is rusted tight.
Tuesday, April 30th, 2013 AT 3:36 PM